The present invention relates to fluid handling systems, and more specifically to a multi-way valve unit having a regulated main valve, and an unregulated minimum bypass valve.
One common method of regulating gas flow is with a diaphragm valve. While many mechanisms exist to control the diaphragm valve, one popular method uses the inlet port pressure to control the position of a valve seat-engaging member relative to the valve seat, movement of the seat-engaging member being controlled by a valve diaphragm. Basically, this is accomplished by creating a pressure differential from one side of the valve diaphragm to the other sufficient to displace the diaphragm and the associated seat-engaging member. In simplest form, the seat-engaging member may be an integral part of the diaphragm. In more complicated systems, the valve diaphragm is mechanically linked to a separate seat-engaging member. The distance between the valve seat and the seat engaging member determines the valve opening, and thus the gas pressure at the outlet port.
A disadvantage of this control method is that any undesirable variations in the inlet pressure will be reflected in the outlet pressure, especially at low outlet pressures. For higher outlet gas pressures, these variations become negligible. Specifically, conventional diaphragm operated valves cannot provide acceptable pressure characteristics under approximately 0.3" water column (w.c.). Thus the operating range of the diaphragm valve is substantially limited at low pressures by these inlet pressure variations.
Many popular gas control techniques would benefit from a valve system providing an extended operating pressure range at low pressures. One common example is so-called "on-demand" gas heating systems. In on-demand systems, fuel gas is provided only when there is a demand for heat. The demand is met by supplying only enough gas to exactly meet the needs of the application. For example, in a gas system for hot water supply, low gas pressure may be used to provide hot water to a sink, but high pressure will be provided if the shower is turned on. As a second example, in a space heating system, low gas pressure may be provided to raise the temperature by several degrees, but high gas pressure will be provided if the temperature in the controlled space is substantially below the desired temperature.
Valve systems providing both high and low controlled gas pressure also find application in slow-opening gas valve systems. Slow-opening gas valves have become a common means of improving the start-up characteristics of gas burner systems. In these applications, ramping to full gas pressure follows an initially low gas pressure period. In systems without improved start-up, initial full gas pressure may cause a dangerous gas flash to occur upon ignition. Although this flash is usually contained within the burner chamber, it also typically causes uncombusted gas to be propelled out of the burner chamber. By using low gas pressure on start-up, the initial start-up flash is essentially eliminated. This improves both the safety and the efficiency of the burner system.
Several workable slow-opening solutions exist which provide initial low gas pressure. U.S. Pat. No. 4,790,352 to Dietiker, et al is one such patent. In the Dietiker patent, gas pressure is ramped to full gas pressure, thus preventing the aforementioned flash problem. U.S. Pat. No. 4,254,796 to Kelly describes another such system. In the Kelly patent, low gas pressure is only provided for a short initial period followed by full valve opening. Neither system however, can provide continuous regulated gas pressure control at low pressures.
Other systems may exist to provide separate low pressure and high pressure gas supply. These systems do not however provide integrated solutions for controlled low gas pressure and high regulated gas pressure in the same valve system.
Accordingly, the applicants have endeavored to provide a gas valve system which smoothly integrates a diaphragm operated valve capable of over approximately 0.3" w.c. pressure regulation with a valve capable of controlled unregulated pressure under approximately 0.3" w.c. Furthermore, the applicants have provided for common control of the high and low gas pressure in a system which minimizes overall component count, and which achieves a smooth transition from low pressure to high pressure operation.